Wireless communication environment in recent years faces a problem of a rapid increase in data traffic. Hence, in 3GPP, installing a large number of small cells in a macro cell to increase network density, thereby distributing traffic, has been under study. Such a technology utilizing small cells is referred to as small cell enhancement. Note that small cells may conceptually include various types of cells (e.g., a femto cell, a nano cell, a pica cell, a micro cell, and the like) that are smaller than a macro cell and are arranged to overlap a macro cell.
In addition, as one way to expand radio resources, utilization of a frequency band of 6 GHz or more, which is called a millimeter-wave band, has been under study. However, since the millimeter-wave band has strong straightness and exhibits large radio propagation attenuation, utilization in a small cell smaller than a macro cell is expected. Furthermore, since the range of the millimeter-wave band is very large, all frequency bands are not assumed to be licensed bands and a considerable number of frequency bands are assumed to be unlicensed bands for which secondary use is possible.
As a technology related to secondary use of frequencies, for example, Patent Literature 1 mentioned below discloses a mechanism in which information is exchanged between a plurality of networks operated by different service providers and thereby a service provider can ascertain whether a frequency band of another service provider can be utilized.